Imaging radiation panels for detecting imagewise intensity modulated radiation such as x-ray radiation and for producing an electronic signal representing the image in the modulated radiation which may be digitized, stored, computer enhanced and subsequently displayed as a visible image in a number of different display media are well known. Such panels include an array of a plurality of sensors able to convert incident radiation directly to an electrical charge indicative of the intensity of the incident radiation. Typically such sensors comprise a complex structure which includes a radiation detection element and a charge storage element. The radiation detection element may be a photodiode operating together with a scintillation layer to detect photons emitted when radiation strikes the scintillation layer and produce a charge proportional to the photon intensity, or it may be a photoconductor which produces electrical charges directly when exposed to radiation and a charge collecting electrode to collect such charges. The charges so produced are typically stored in some storage device, most often a charge storage capacitor. Typical such panels are described in, for example: Jeromin, U.S. Pat. No. 5,168,160; Lee, U.S. Pat. No. 5,319,206; Lee, U.S. Pat. No. 5,652,430; Jeromin et al. U.S. Pat. 5,381,014, Hughes et al. U.S. Pat. No. 5,315,101 and Tran, U.S. Pat. No. 5,254,480.
Regardless of the particular type of sensor used, be it a photoconductor type or a photosensitive layer, most panels also employ a field electrode which usually extends uninterrupted over all sensors to apply a biasing field to the individual sensors. Also regardless of the particular sensor type used, most panels include electronic circuitry for addressing each sensor and recovering the charge stored therein in a manner which permits an image reconstruction sensor by sensor, each sensor forming a picture element or PIXEL of the complete image. Again the most commonly elements used to address each sensor are MOSFET switches, and are constructed using thin film technology, thereby often being referred to as TFT switches.
Associated with the sensors are sensitive electronics in the form of a plurality of integrated circuit chips, usually integrating amplifiers which receive the charge from the sensors and amplify it to produce a usable electronic signal proportional to the stored charge generated by the incident radiation.
The amount of charge that forms the initial signal prior to amplification is exceedingly small. The amplifiers are therefore most often placed as close as possible to the sensors, which in practical terms means along the panel edges right next to the beginning of the outermost column and line of the sensor array. As was stated previously, in most structures the sensor array is covered by the field electrode, which is co-extensive with the sensor array perimeter. Therefore the amplifiers tend to be in very close proximity to this field electrode. Depending on the sensor exact nature and the mode of operating the panel, a biasing voltage is applied to this field electrode and this biasing voltage may be raised to quite high levels. When this voltage is high, the amplifiers are susceptible to current leakage between the field electrode and the amplifier input and occasionally to voltage breakdown between the field electrode edge and the amplifier input leads. Typically the detector is enclosed in a container. The field electrode may generate ionized air that is confined by the container and that can drift over the amplifiers. The input signal to the amplifier may thus receive a noise spike or other noise signals. Such noise spikes or signals show on the image as a series of lines that are unacceptable to consumers of the radiation detection panels because the lines tend to obscure the actual image.
It is an object, therefore, of the present invention to provide a panel comprising a plurality of sensors, of the type which includes a field electrode, capable of creating an image that is substantially free of unacceptable noise lines.